German patent document DE 196 26 689 discusses a method and a device for monitoring an injection system. It discusses a so-called common rail system, in which at least one injector injects fuel from a high-pressure area into a combustion chamber of an internal combustion engine. The pressure in the high-pressure area is controllable via at least one actuator. In addition, a sensor via which the pressure in the high-pressure area is detected is usually provided. The pressure in the high-pressure area is detected against the background of the rail pressure, as the pressure in the high-pressure area is also referred to, being regulated at a predefined level. Furthermore, the rail pressure is required to implement an accurate metering of fuel.
In the event of a failure of this rail pressure sensor, suitable measures must usually be implemented. If such an error occurs, the high-pressure pump is usually put in a “full delivery” mode. Therefore, an excess pressure is usually established in the high-pressure area. This excess pressure results in the opening of a pressure-limiting valve, which opens a connection to the low-pressure area when a certain rail pressure is exceeded in the high-pressure area. The opening pressure of the pressure-limiting valve is typically 200 to 400 bar above the maximum system pressure. After opening the pressure-limiting valve, a rail pressure of approximately 700 bar is established virtually independently of the delivery rate of the high-pressure pump. The entire injection system, even without a rail pressure sensor, is thus in a defined state and is available for emergency operation.
In certain operating states or when there is a defect in the pressure-limiting valve, it may occur that this pressure-limiting valve does not open. This results in an increased rail pressure. Such an increased rail pressure may in turn result in damage to the injector in particular.